Recently, various types of audio sources have been distributed and provided in open markets; hence, 5.1-channel multi-channel audio signals are recorded on DVDs (digital versatile disks), for example. Audio digital surround systems for reproducing audio sources have become common in households. FIG. 11 is a plan view showing an example of arrangement of speakers in an audio digital surround system, wherein reference symbol Zone designates a listening room for use in audio surround playback; reference symbol U designates a listening position; reference symbol SP-L designates a speaker for use in playback of a main left signal L; reference symbol SP-R designates a speaker for use in playback of a main right signal R; reference symbol SP-C designates a speaker for use in playback of a center signal C; reference symbol SP-SL designates a speaker for use in playback of a rear left signal SL; reference symbol SP-SR designates a speaker for use in playback of a rear right signal SR; reference symbol SP-SW designates a sub-woofer for use in playback of a sub-woofer signal (a low-frequency signal) LFE; and reference symbol MON designates a video device such as a television receiver.
The audio digital surround system of FIG. 11 can effectively realize various sound fields in the listening room Zone. However, this audio digital surround system, in which plural speakers are spread out and distributed in the listening room Zone, suffers from various drawbacks in that in order to arrange the rear speakers SP-SL and SP-SR for surround playback in the rear of the listening position U, wiring lengths therebetween must be increased, and in that the arrangement of the rear speakers SP-SL and SP-SR is limited due to the overall shape of the listening room Zone and due to the arrangement of furniture.
As a countermeasure solving the aforementioned drawbacks, there is provided an audio surround system in which rear speakers are each constituted using directional speakers each having sharp directivity and are arranged in front of the listening position, while a sound reflection board is arranged in the rear of the listening position. This is disclosed in Japanese Unexamined Patent Application Publication No. H06-178379, for example. Herein, surround-channel sounds emitted from directional speakers are reflected on the sound reflection board, thus demonstrating effects similar to those realized by arranging rear speakers in the rear of the listening position. FIG. 12 is a plan view showing an example of arrangement of speakers in the audio surround system disclosed in the aforementioned Japanese unexamined patent application publication, wherein reference symbols B-L and B-R designate sound reflection boards.
It is possible to use another method as shown in FIG. 13, in which a rear wall surface positioned in the rear of the listening position is used as a sound reflection board. For example, Japanese Unexamined Patent Application Publication No. H03-159500 discloses a three-dimensional stereo playback method in which array speakers are used to create virtual sound sources in a prescribed space. By use of this technology, it is possible to produce virtual speakers in the rear of the listening position.
As described above, it is possible to produce virtual speakers in the rear of the listening position by arranging sound reflection boards in the rear of the listening position or by using wall surfaces of a listening room as sound reflection boards. However, these methods may have difficulty in realizing virtual speakers having good audio characteristics because audio characteristics of the wall surfaces or sound reflection boards influence audio characteristics of the virtual speakers.
This invention is made to solve the aforementioned problems; and it is an object of the invention to provide an audio characteristic correction system adapted to an audio surround system in which sounds emitted from directional speakers are reflected on wall surfaces of a prescribed room or on sound reflection boards so as to produce virtual speakers, wherein audio characteristics of the wall surfaces or sound reflection boards are corrected for so as to improve audio characteristics of the virtual speakers.